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Tether inductance issue

Has people ever experienced signal delays or connection issues via the tether due to the inductance of the wire? We have long tether (150m) and when testing the vehicle in a pool, most of the tether is coiled up, which makes it act like a giant inductor. Has this been known to produce signal delays or disrupt video feed between ROV and QGroundControl?
The reason I ask is we are seeing video lag (half a second) and pixelated/gray video frame every so often and we are not sure why. Trying to get some intuition w.r.t. the cause, whether it’s due to the physical link or software.
Thanks in advance.

Hi @searover2021,

Ethernet uses a differential signal, which allows for what’s called “common mode rejection”. Basically that means that any noise or signal deviation that happens equally to both wires in a pair gets cancelled out (rejected) and doesn’t have an effect on the resulting measured signal at the end. The tether uses CAT5 cable, which comes as twisted pairs. Each wire in a pair should be the same resistance (generally achieved with same length & gauge), and the twists help to make sure both wires get equal exposure to noise from nearby electrical signals (e.g. the other pairs, and inductance of the whole cable). There’s a more detailed explanation in this blog post if you’re interested :slight_smile:

Try the video troubleshooting steps and let us know what you find :slight_smile:

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I use 300 m BR tether in one setup, using two pairs for 240V AC power and one pair for telemetry/video.
All that 300m curled up in a round bucket with no problem att all.
So I guess your problem is not inductance.

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